On Fri, Aug 23, 2013 at 6:02 AM, Chris Barker - NOAA Federal <chris.barker@noaa.gov> wrote:

Hi folks,

I had thought that maybe a numpy.long dtype was a system
(compiler)-native C long.

But on both 32 and 64 bit python on OS-X, it seems to be 64 bit. I'm
pretty sure that on OS-X 32 bit, a C long is 32 bits. (gdd, of course)

I don't have other machines to test on , but as the MS compilers and
gcc do different things with a C long on 64 bit platforms, I"m curious
how numpy defines it.

In general, I prefer the "explicit is better than implicit" approach
and use, e.g. int32 and int64. However, in this case, we are using
Cython, and calling C code that used "long" -- so what I want is
"whatever the compiler thinks is a long" -- is there a way to do that
without my own kludgy platform-dependent code?

I note that the Cython numpy.pxd assigns:

ctypedef signed long npy_long

Is that a bug? (or maybe npy_long is not supposed to match np.long....

npy_long is indeed just an alias to C long, np.long is an alias to python's long:

arch -32 python -c "import numpy as np; print np.dtype(np.int); print np.dtype(np.long)"

int32

int64

arch -64 python -c "import numpy as np; print np.dtype(np.int); print np.dtype(np.long)"

int64

and python -c "import numpy as np; print np.long is long" will print True

All this is on python 2.7, I am not sure how/if that changes on python 3 (that consolidated python int/long).

David

-Chris

--

Christopher Barker, Ph.D.
Oceanographer

Emergency Response Division
NOAA/NOS/OR&R (206) 526-6959 voice
7600 Sand Point Way NE (206) 526-6329 fax
Seattle, WA 98115 (206) 526-6317 main reception

Chris.Barker@noaa.gov
_______________________________________________
NumPy-Discussion mailing list
NumPy-Discussion@scipy.org
http://mail.scipy.org/mailman/listinfo/numpy-discussion